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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Dynamic function tracer architecture backend.
4 *
5 * Copyright IBM Corp. 2009,2014
6 *
7 * Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
8 */
9
10#include <linux/moduleloader.h>
11#include <linux/hardirq.h>
12#include <linux/uaccess.h>
13#include <linux/ftrace.h>
14#include <linux/kernel.h>
15#include <linux/types.h>
16#include <linux/kprobes.h>
17#include <trace/syscall.h>
18#include <asm/asm-offsets.h>
19#include <asm/text-patching.h>
20#include <asm/cacheflush.h>
21#include <asm/ftrace.lds.h>
22#include <asm/nospec-branch.h>
23#include <asm/set_memory.h>
24#include "entry.h"
25#include "ftrace.h"
26
27/*
28 * To generate function prologue either gcc's hotpatch feature (since gcc 4.8)
29 * or a combination of -pg -mrecord-mcount -mnop-mcount -mfentry flags
30 * (since gcc 9 / clang 10) is used.
31 * In both cases the original and also the disabled function prologue contains
32 * only a single six byte instruction and looks like this:
33 * > brcl 0,0 # offset 0
34 * To enable ftrace the code gets patched like above and afterwards looks
35 * like this:
36 * > brasl %r0,ftrace_caller # offset 0
37 *
38 * The instruction will be patched by ftrace_make_call / ftrace_make_nop.
39 * The ftrace function gets called with a non-standard C function call ABI
40 * where r0 contains the return address. It is also expected that the called
41 * function only clobbers r0 and r1, but restores r2-r15.
42 * For module code we can't directly jump to ftrace caller, but need a
43 * trampoline (ftrace_plt), which clobbers also r1.
44 */
45
46void *ftrace_func __read_mostly = ftrace_stub;
47struct ftrace_insn {
48 u16 opc;
49 s32 disp;
50} __packed;
51
52#ifdef CONFIG_MODULES
53static char *ftrace_plt;
54#endif /* CONFIG_MODULES */
55
56static const char *ftrace_shared_hotpatch_trampoline(const char **end)
57{
58 const char *tstart, *tend;
59
60 tstart = ftrace_shared_hotpatch_trampoline_br;
61 tend = ftrace_shared_hotpatch_trampoline_br_end;
62#ifdef CONFIG_EXPOLINE
63 if (!nospec_disable) {
64 tstart = ftrace_shared_hotpatch_trampoline_exrl;
65 tend = ftrace_shared_hotpatch_trampoline_exrl_end;
66 }
67#endif /* CONFIG_EXPOLINE */
68 if (end)
69 *end = tend;
70 return tstart;
71}
72
73bool ftrace_need_init_nop(void)
74{
75 return true;
76}
77
78int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)
79{
80 static struct ftrace_hotpatch_trampoline *next_vmlinux_trampoline =
81 __ftrace_hotpatch_trampolines_start;
82 static const char orig[6] = { 0xc0, 0x04, 0x00, 0x00, 0x00, 0x00 };
83 static struct ftrace_hotpatch_trampoline *trampoline;
84 struct ftrace_hotpatch_trampoline **next_trampoline;
85 struct ftrace_hotpatch_trampoline *trampolines_end;
86 struct ftrace_hotpatch_trampoline tmp;
87 struct ftrace_insn *insn;
88 const char *shared;
89 s32 disp;
90
91 BUILD_BUG_ON(sizeof(struct ftrace_hotpatch_trampoline) !=
92 SIZEOF_FTRACE_HOTPATCH_TRAMPOLINE);
93
94 next_trampoline = &next_vmlinux_trampoline;
95 trampolines_end = __ftrace_hotpatch_trampolines_end;
96 shared = ftrace_shared_hotpatch_trampoline(NULL);
97#ifdef CONFIG_MODULES
98 if (mod) {
99 next_trampoline = &mod->arch.next_trampoline;
100 trampolines_end = mod->arch.trampolines_end;
101 shared = ftrace_plt;
102 }
103#endif
104
105 if (WARN_ON_ONCE(*next_trampoline >= trampolines_end))
106 return -ENOMEM;
107 trampoline = (*next_trampoline)++;
108
109 /* Check for the compiler-generated fentry nop (brcl 0, .). */
110 if (WARN_ON_ONCE(memcmp((const void *)rec->ip, &orig, sizeof(orig))))
111 return -EINVAL;
112
113 /* Generate the trampoline. */
114 tmp.brasl_opc = 0xc015; /* brasl %r1, shared */
115 tmp.brasl_disp = (shared - (const char *)&trampoline->brasl_opc) / 2;
116 tmp.interceptor = FTRACE_ADDR;
117 tmp.rest_of_intercepted_function = rec->ip + sizeof(struct ftrace_insn);
118 s390_kernel_write(trampoline, &tmp, sizeof(tmp));
119
120 /* Generate a jump to the trampoline. */
121 disp = ((char *)trampoline - (char *)rec->ip) / 2;
122 insn = (struct ftrace_insn *)rec->ip;
123 s390_kernel_write(&insn->disp, &disp, sizeof(disp));
124
125 return 0;
126}
127
128static struct ftrace_hotpatch_trampoline *ftrace_get_trampoline(struct dyn_ftrace *rec)
129{
130 struct ftrace_hotpatch_trampoline *trampoline;
131 struct ftrace_insn insn;
132 s64 disp;
133 u16 opc;
134
135 if (copy_from_kernel_nofault(&insn, (void *)rec->ip, sizeof(insn)))
136 return ERR_PTR(-EFAULT);
137 disp = (s64)insn.disp * 2;
138 trampoline = (void *)(rec->ip + disp);
139 if (get_kernel_nofault(opc, &trampoline->brasl_opc))
140 return ERR_PTR(-EFAULT);
141 if (opc != 0xc015)
142 return ERR_PTR(-EINVAL);
143 return trampoline;
144}
145
146int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
147 unsigned long addr)
148{
149 struct ftrace_hotpatch_trampoline *trampoline;
150 u64 old;
151
152 trampoline = ftrace_get_trampoline(rec);
153 if (IS_ERR(trampoline))
154 return PTR_ERR(trampoline);
155 if (get_kernel_nofault(old, &trampoline->interceptor))
156 return -EFAULT;
157 if (old != old_addr)
158 return -EINVAL;
159 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
160 return 0;
161}
162
163static int ftrace_patch_branch_mask(void *addr, u16 expected, bool enable)
164{
165 u16 old;
166 u8 op;
167
168 if (get_kernel_nofault(old, addr))
169 return -EFAULT;
170 if (old != expected)
171 return -EINVAL;
172 /* set mask field to all ones or zeroes */
173 op = enable ? 0xf4 : 0x04;
174 s390_kernel_write((char *)addr + 1, &op, sizeof(op));
175 return 0;
176}
177
178int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
179 unsigned long addr)
180{
181 /* Expect brcl 0xf,... */
182 return ftrace_patch_branch_mask((void *)rec->ip, 0xc0f4, false);
183}
184
185int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
186{
187 struct ftrace_hotpatch_trampoline *trampoline;
188
189 trampoline = ftrace_get_trampoline(rec);
190 if (IS_ERR(trampoline))
191 return PTR_ERR(trampoline);
192 s390_kernel_write(&trampoline->interceptor, &addr, sizeof(addr));
193 /* Expect brcl 0x0,... */
194 return ftrace_patch_branch_mask((void *)rec->ip, 0xc004, true);
195}
196
197int ftrace_update_ftrace_func(ftrace_func_t func)
198{
199 ftrace_func = func;
200 return 0;
201}
202
203void arch_ftrace_update_code(int command)
204{
205 ftrace_modify_all_code(command);
206}
207
208void ftrace_arch_code_modify_post_process(void)
209{
210 /*
211 * Flush any pre-fetched instructions on all
212 * CPUs to make the new code visible.
213 */
214 text_poke_sync_lock();
215}
216
217#ifdef CONFIG_MODULES
218
219static int __init ftrace_plt_init(void)
220{
221 const char *start, *end;
222
223 ftrace_plt = module_alloc(PAGE_SIZE);
224 if (!ftrace_plt)
225 panic("cannot allocate ftrace plt\n");
226
227 start = ftrace_shared_hotpatch_trampoline(&end);
228 memcpy(ftrace_plt, start, end - start);
229 set_memory_rox((unsigned long)ftrace_plt, 1);
230 return 0;
231}
232device_initcall(ftrace_plt_init);
233
234#endif /* CONFIG_MODULES */
235
236#ifdef CONFIG_FUNCTION_GRAPH_TRACER
237/*
238 * Hook the return address and push it in the stack of return addresses
239 * in current thread info.
240 */
241unsigned long prepare_ftrace_return(unsigned long ra, unsigned long sp,
242 unsigned long ip)
243{
244 if (unlikely(ftrace_graph_is_dead()))
245 goto out;
246 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
247 goto out;
248 ip -= MCOUNT_INSN_SIZE;
249 if (!function_graph_enter(ra, ip, 0, (void *) sp))
250 ra = (unsigned long) return_to_handler;
251out:
252 return ra;
253}
254NOKPROBE_SYMBOL(prepare_ftrace_return);
255
256/*
257 * Patch the kernel code at ftrace_graph_caller location. The instruction
258 * there is branch relative on condition. To enable the ftrace graph code
259 * block, we simply patch the mask field of the instruction to zero and
260 * turn the instruction into a nop.
261 * To disable the ftrace graph code the mask field will be patched to
262 * all ones, which turns the instruction into an unconditional branch.
263 */
264int ftrace_enable_ftrace_graph_caller(void)
265{
266 int rc;
267
268 /* Expect brc 0xf,... */
269 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa7f4, false);
270 if (rc)
271 return rc;
272 text_poke_sync_lock();
273 return 0;
274}
275
276int ftrace_disable_ftrace_graph_caller(void)
277{
278 int rc;
279
280 /* Expect brc 0x0,... */
281 rc = ftrace_patch_branch_mask(ftrace_graph_caller, 0xa704, true);
282 if (rc)
283 return rc;
284 text_poke_sync_lock();
285 return 0;
286}
287
288#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
289
290#ifdef CONFIG_KPROBES_ON_FTRACE
291void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
292 struct ftrace_ops *ops, struct ftrace_regs *fregs)
293{
294 struct kprobe_ctlblk *kcb;
295 struct pt_regs *regs;
296 struct kprobe *p;
297 int bit;
298
299 bit = ftrace_test_recursion_trylock(ip, parent_ip);
300 if (bit < 0)
301 return;
302
303 regs = ftrace_get_regs(fregs);
304 p = get_kprobe((kprobe_opcode_t *)ip);
305 if (!regs || unlikely(!p) || kprobe_disabled(p))
306 goto out;
307
308 if (kprobe_running()) {
309 kprobes_inc_nmissed_count(p);
310 goto out;
311 }
312
313 __this_cpu_write(current_kprobe, p);
314
315 kcb = get_kprobe_ctlblk();
316 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
317
318 instruction_pointer_set(regs, ip);
319
320 if (!p->pre_handler || !p->pre_handler(p, regs)) {
321
322 instruction_pointer_set(regs, ip + MCOUNT_INSN_SIZE);
323
324 if (unlikely(p->post_handler)) {
325 kcb->kprobe_status = KPROBE_HIT_SSDONE;
326 p->post_handler(p, regs, 0);
327 }
328 }
329 __this_cpu_write(current_kprobe, NULL);
330out:
331 ftrace_test_recursion_unlock(bit);
332}
333NOKPROBE_SYMBOL(kprobe_ftrace_handler);
334
335int arch_prepare_kprobe_ftrace(struct kprobe *p)
336{
337 p->ainsn.insn = NULL;
338 return 0;
339}
340#endif
1/*
2 * Dynamic function tracer architecture backend.
3 *
4 * Copyright IBM Corp. 2009,2014
5 *
6 * Author(s): Heiko Carstens <heiko.carstens@de.ibm.com>,
7 * Martin Schwidefsky <schwidefsky@de.ibm.com>
8 */
9
10#include <linux/moduleloader.h>
11#include <linux/hardirq.h>
12#include <linux/uaccess.h>
13#include <linux/ftrace.h>
14#include <linux/kernel.h>
15#include <linux/types.h>
16#include <linux/kprobes.h>
17#include <trace/syscall.h>
18#include <asm/asm-offsets.h>
19#include <asm/cacheflush.h>
20#include "entry.h"
21
22/*
23 * The mcount code looks like this:
24 * stg %r14,8(%r15) # offset 0
25 * larl %r1,<&counter> # offset 6
26 * brasl %r14,_mcount # offset 12
27 * lg %r14,8(%r15) # offset 18
28 * Total length is 24 bytes. Only the first instruction will be patched
29 * by ftrace_make_call / ftrace_make_nop.
30 * The enabled ftrace code block looks like this:
31 * > brasl %r0,ftrace_caller # offset 0
32 * larl %r1,<&counter> # offset 6
33 * brasl %r14,_mcount # offset 12
34 * lg %r14,8(%r15) # offset 18
35 * The ftrace function gets called with a non-standard C function call ABI
36 * where r0 contains the return address. It is also expected that the called
37 * function only clobbers r0 and r1, but restores r2-r15.
38 * For module code we can't directly jump to ftrace caller, but need a
39 * trampoline (ftrace_plt), which clobbers also r1.
40 * The return point of the ftrace function has offset 24, so execution
41 * continues behind the mcount block.
42 * The disabled ftrace code block looks like this:
43 * > jg .+24 # offset 0
44 * larl %r1,<&counter> # offset 6
45 * brasl %r14,_mcount # offset 12
46 * lg %r14,8(%r15) # offset 18
47 * The jg instruction branches to offset 24 to skip as many instructions
48 * as possible.
49 * In case we use gcc's hotpatch feature the original and also the disabled
50 * function prologue contains only a single six byte instruction and looks
51 * like this:
52 * > brcl 0,0 # offset 0
53 * To enable ftrace the code gets patched like above and afterwards looks
54 * like this:
55 * > brasl %r0,ftrace_caller # offset 0
56 */
57
58unsigned long ftrace_plt;
59
60static inline void ftrace_generate_orig_insn(struct ftrace_insn *insn)
61{
62#ifdef CC_USING_HOTPATCH
63 /* brcl 0,0 */
64 insn->opc = 0xc004;
65 insn->disp = 0;
66#else
67 /* stg r14,8(r15) */
68 insn->opc = 0xe3e0;
69 insn->disp = 0xf0080024;
70#endif
71}
72
73static inline int is_kprobe_on_ftrace(struct ftrace_insn *insn)
74{
75#ifdef CONFIG_KPROBES
76 if (insn->opc == BREAKPOINT_INSTRUCTION)
77 return 1;
78#endif
79 return 0;
80}
81
82static inline void ftrace_generate_kprobe_nop_insn(struct ftrace_insn *insn)
83{
84#ifdef CONFIG_KPROBES
85 insn->opc = BREAKPOINT_INSTRUCTION;
86 insn->disp = KPROBE_ON_FTRACE_NOP;
87#endif
88}
89
90static inline void ftrace_generate_kprobe_call_insn(struct ftrace_insn *insn)
91{
92#ifdef CONFIG_KPROBES
93 insn->opc = BREAKPOINT_INSTRUCTION;
94 insn->disp = KPROBE_ON_FTRACE_CALL;
95#endif
96}
97
98int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
99 unsigned long addr)
100{
101 return 0;
102}
103
104int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
105 unsigned long addr)
106{
107 struct ftrace_insn orig, new, old;
108
109 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
110 return -EFAULT;
111 if (addr == MCOUNT_ADDR) {
112 /* Initial code replacement */
113 ftrace_generate_orig_insn(&orig);
114 ftrace_generate_nop_insn(&new);
115 } else if (is_kprobe_on_ftrace(&old)) {
116 /*
117 * If we find a breakpoint instruction, a kprobe has been
118 * placed at the beginning of the function. We write the
119 * constant KPROBE_ON_FTRACE_NOP into the remaining four
120 * bytes of the original instruction so that the kprobes
121 * handler can execute a nop, if it reaches this breakpoint.
122 */
123 ftrace_generate_kprobe_call_insn(&orig);
124 ftrace_generate_kprobe_nop_insn(&new);
125 } else {
126 /* Replace ftrace call with a nop. */
127 ftrace_generate_call_insn(&orig, rec->ip);
128 ftrace_generate_nop_insn(&new);
129 }
130 /* Verify that the to be replaced code matches what we expect. */
131 if (memcmp(&orig, &old, sizeof(old)))
132 return -EINVAL;
133 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
134 return 0;
135}
136
137int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
138{
139 struct ftrace_insn orig, new, old;
140
141 if (probe_kernel_read(&old, (void *) rec->ip, sizeof(old)))
142 return -EFAULT;
143 if (is_kprobe_on_ftrace(&old)) {
144 /*
145 * If we find a breakpoint instruction, a kprobe has been
146 * placed at the beginning of the function. We write the
147 * constant KPROBE_ON_FTRACE_CALL into the remaining four
148 * bytes of the original instruction so that the kprobes
149 * handler can execute a brasl if it reaches this breakpoint.
150 */
151 ftrace_generate_kprobe_nop_insn(&orig);
152 ftrace_generate_kprobe_call_insn(&new);
153 } else {
154 /* Replace nop with an ftrace call. */
155 ftrace_generate_nop_insn(&orig);
156 ftrace_generate_call_insn(&new, rec->ip);
157 }
158 /* Verify that the to be replaced code matches what we expect. */
159 if (memcmp(&orig, &old, sizeof(old)))
160 return -EINVAL;
161 s390_kernel_write((void *) rec->ip, &new, sizeof(new));
162 return 0;
163}
164
165int ftrace_update_ftrace_func(ftrace_func_t func)
166{
167 return 0;
168}
169
170int __init ftrace_dyn_arch_init(void)
171{
172 return 0;
173}
174
175static int __init ftrace_plt_init(void)
176{
177 unsigned int *ip;
178
179 ftrace_plt = (unsigned long) module_alloc(PAGE_SIZE);
180 if (!ftrace_plt)
181 panic("cannot allocate ftrace plt\n");
182 ip = (unsigned int *) ftrace_plt;
183 ip[0] = 0x0d10e310; /* basr 1,0; lg 1,10(1); br 1 */
184 ip[1] = 0x100a0004;
185 ip[2] = 0x07f10000;
186 ip[3] = FTRACE_ADDR >> 32;
187 ip[4] = FTRACE_ADDR & 0xffffffff;
188 set_memory_ro(ftrace_plt, 1);
189 return 0;
190}
191device_initcall(ftrace_plt_init);
192
193#ifdef CONFIG_FUNCTION_GRAPH_TRACER
194/*
195 * Hook the return address and push it in the stack of return addresses
196 * in current thread info.
197 */
198unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip)
199{
200 struct ftrace_graph_ent trace;
201
202 if (unlikely(ftrace_graph_is_dead()))
203 goto out;
204 if (unlikely(atomic_read(¤t->tracing_graph_pause)))
205 goto out;
206 ip -= MCOUNT_INSN_SIZE;
207 trace.func = ip;
208 trace.depth = current->curr_ret_stack + 1;
209 /* Only trace if the calling function expects to. */
210 if (!ftrace_graph_entry(&trace))
211 goto out;
212 if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
213 goto out;
214 parent = (unsigned long) return_to_handler;
215out:
216 return parent;
217}
218NOKPROBE_SYMBOL(prepare_ftrace_return);
219
220/*
221 * Patch the kernel code at ftrace_graph_caller location. The instruction
222 * there is branch relative on condition. To enable the ftrace graph code
223 * block, we simply patch the mask field of the instruction to zero and
224 * turn the instruction into a nop.
225 * To disable the ftrace graph code the mask field will be patched to
226 * all ones, which turns the instruction into an unconditional branch.
227 */
228int ftrace_enable_ftrace_graph_caller(void)
229{
230 u8 op = 0x04; /* set mask field to zero */
231
232 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
233 return 0;
234}
235
236int ftrace_disable_ftrace_graph_caller(void)
237{
238 u8 op = 0xf4; /* set mask field to all ones */
239
240 s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
241 return 0;
242}
243
244#endif /* CONFIG_FUNCTION_GRAPH_TRACER */